The z-index attribute is not effective!!!

[FEsujian]

https://stackblitz.com/github/Joepocalyptic/nuxt-particles?file=playground%2Fapp.vue

I found that in the project
FullScreen:{
Enable: true,
ZIndex: -1
}
invalid
There is no z-index attribute in style

There is a bug. The owner have no time to fix it, at this time.
I hope he will get back to me soon when he was fixing it.